The southwestern desert regions are credited with harboring several genera of snakes whose grooved back teeth indicate that they may have poisonous properties. Of these, the Sonora lyre snake[11] (Trimorphodon lambda) and the Mexican vine snake (Oxybelis aeneus auratus) are the only species of sufficient size to be considered as even remotely dangerous to mankind. Species of the genera Tantilla (black-headed snake), Hypsiglena, and Sonora are too small and too difficult for the amateur to identify to be considered in this publication.
Gila monster
(Heloderma suspectum)
More conflicting statements are made about the Gila (HEE-lah) monster than about any other desert reptile. Some persons insist that it is not poisonous, others are sure that even its breath is poisonous: that it spits or blows its poison: that the animal has no anal opening, hence undigested fecal matter remains in the body, decays, and is the basis of its poison; and so on.
Gila monster (Heloderma suspectum).
Here are the facts. The lizard is poisonous and its bite may be serious, possibly fatal[13]. Its breath is not poisonous, and although the animal seems to have a chronic case of halitosis, this has nothing to do with its dangerous properties. It does not spit poison, but when angered it frequently hisses, the outcoming blast of air sometimes carrying droplets of saliva. It has a normal anal opening and voids fecal matter in a perfectly normal manner. It is not a walking septic tank as many persons believe.
Largest of the lizards native to the United States, and the only species found in this country which is poisonous, the Gila monster rarely attains a length of 2 feet. Average specimens are smaller. Its beady skin, heavy body, short legs, and waddling gait set it apart from all other lizards except its close relative, the also poisonous Heloderma horridum of Mexico. The Gila Monster is a spectacular black and corral color, while the other is black and yellow.
Gila monsters are found in southern Arizona, their range extending northwestward into the southern tip of Nevada and southwestern Utah.
Underside of Gila monster showing anal opening. This photograph is advanced as proof that the Gila monster is a perfectly normal creature in this respect. (Photo courtesy of Poisonous Animals Research Laboratory, Tempe, Arizona)